This invention relates to an integrated reactor and extraction process and operating techniques for converting crude methanol or similar lower aliphatic alcohols to high octane gasoline and methyl tertiary-alkyl ethers, such as MTBE. In particular, this invention relates to an improvement in utilizing methanol-to-gasoline (MTG) processes and operating systems for converting crude methanol to valuable products by etherifying lower branched olefins, such as C.sub.4 -C.sub.5 normally liquid iso-olefins.
Technical progress of the commercial methanol-to-gasoline MTG process has provided an important synthetic fuel source. Also, there has been considerable development of processes synthetic alkyl tertiary-alkyl ethers as octane boosters in place of conventional lead additives in gasoline. The etherification processes for the production of methyl tertiary alkyl ethers, in particular methyl t-butyl ether (MTBE) and t-amyl methyl ether (TAME) have been the focus of considerable research attention to resolve certain limitations in the etherification process with respect to the opportunity to drive the equilibrium dependent etherification reaction to completion by conducting etherification in the presence of excess methanol. It is know that recovering unreacted methanol by conventional separation and extraction techniques imposes severe economic burdens on the etherification process.
Recognizing the common feedstock (e.g., methanol) for the synthetic production of gasoline as well as the production of methyl tertiary alkyl octane boosting ethers, research workers have endeavored to combine these processes in a manner to provide a synergistically beneficial integrated process.
It is known that isobutylene and other isoalkenes produced by hydrocarbon cracking may be reacted with methanol, ethanol, isopropanol and other lower aliphatic primary and secondary alcohols over an acidic catalyst to provide tertiary ethers. Methanol is considered the most important C.sub.1 -C.sub.4 oxygenate feedstock because of its widespread availability and low cost. Therefore, primary emphasis herein is placed on MTBE and TAME. Methanol may be readily obtained from coal by gasification to synthesis gas and conversion of the synthesis gas to methanol by well-established industrial processes. As an alternative, the methanol may be obtained from natural gas by other conventional processes, such as steam reforming or partial oxidation to make the intermediate syngas. Crude methanol from such processes usually contains a significant amount of water, usually in the range of 4 to 20 wt. %; however, the present invention is useful for removing water in lesser amounts or greater.
It is an object of the present invention to provide a novel and economic technique for removing excess water from crude methanol feedstocks, including novel reactor systems and equipment for treating oxygenate feedstocks prior to etherification and disposing of raffinate containing methanol. It has been discovered that aqueous methanol streams, such as etherification feedstock extraction raffinate can be economically upgraded to valuable gasoline product by catalytic conversion concurrently with hydrocarbons.